This Program Project brings together investigators from a variety of disciplines who are focusing their divergent backgrounds on the regulation of keratinocyte differentiation. These workers will exploit in vitro and in vivo models, both human and murine, in which keratinocyte differentiation, including permeability barrier formation, can be manipulated precisely. Project #1 will evaluate the role of cornified envelope-associated proteins in permeability barrier function, utilizing a variety of human diseases due to specific mutations in such proteins as well as mouse models in which such proteins or their presumptive regulators have been genetically altered. Project #2 will investigate the role of protein kinase C in mediating calcium regulated differentiation, seeking in this pathway the mechanism by which calcium fails to stimulate differentiation in transformed keratinocytes. Project #3 will explore the role of the EnaC channel in mediating calcium- induce differentiation, investigating the importance of three major channel subunits for different stages of differentiation. Project #4 will focus on the role of omega-hydroxy ceramides in the formation of the lipid-bound envelope and for barrier function, and the role of the omega hydroxylase in the formation of these unique lipid constituents of the stratum corneum. Project #5 will extend prior observations that PPARalpha agonists promote epidermal differentiation by exploring both the molecular regulation of PPARalpha expression, and the importance of PPARalpha, using both keratinocyte cultures and PPARalpha knockout mice. The Cell Culture/Tissue Preparation Core whose activity is essential for the progress of all projects, will continue to provide advice as well as cells and organ cultures to the investigators. The Microscopy and Molecular Histology Laboratory (Morphology Core) will play an increasingly important role as in situ hybridization and immunolocalization at the light and electron microscopic level are utilized by all of the projects. Each investigator will rely upon other members of the group for ideas and specific collaborations, which will broaden the scope, productivity, and depth of each project. This synergy will be fostered by bi-weekly research meetings, an Outside Speakers Program, and the input of our Research Advisory Group. This proposal, then represents a continuation a continuation a continuation of our ongoing, successful effort at building a cohesive, interdisciplinary group aimed at unraveling the regulation of keratinocyte/epidermal differentiation.